View Full Version : iMac 27" - radeon HD 4850 image support

02-24-2010, 02:24 AM

I am trying to run a program which requires OpenCL image support on an iMac core i5 with a radeon HD 4850. Unfortunately, when I am querying the image support of this card with CL_DEVICE_IMAGE_SUPPORT it returns CL_FALSE.
The same query returns CL_TRUE on a mac mini/GeForce 9400M.

The OpenCL drivers are not the same on the different apple computers ? Will the image support on HD 4850 be fixed ?

02-24-2010, 05:42 AM
Different cards have different capabilities. Apple's OpenCL drivers do not support images on ATI Radeon 4xxx series cards, and given Apple's history of not back-porting features, I doubt they ever will. This is why I've stuck with Nvidia GPUs on my machines even though the Radeon is faster for graphics.

My understanding is that the 4xxx series from ATI is really not good for OpenCL, which is why AMD is not even supporting it. The 5xxx series should be a lot better.

02-25-2010, 08:07 AM
Thanks for your response.
I thought that the iMac 27 with HD4850 was a really good environment to do some OpenCL stuffs but not really... bad surprise. I will wait for the mac pro renewal... or maybe will we have a nice surprise with 10.6.3...

03-01-2010, 02:02 PM
I wouldn't count on a software update. The 4800 series don't support things like local memory which is essential for good performance. (It's a hardware issue where they simply don't support the required memory access semantics, so software will never fix the performance issue.) My understanding is that images are somewhat similar. There are undoubtedly technical work arounds to make them function, but they might be so slow that they wouldn't be worth using. Basically I'm sorry to say that the 4800 cards aren't good for anything other than graphics. :(